The quick answer if that if you are going to sell 1/3 of your company for two months of ramen noodles then you don't really think much of it. Already I can tell this guy is not an angel, he smells blood. Plus he's running his company full-time but wants to be a one third partner? When? on weekends? You said you would give numbers but then don't. How much money do you need to survive two months? or is it not two month…
If you don't trust someone, then regardless of how the numbers add up, it's almost certainly a bad idea to have him as a business partner.